In recent years, host strains for production of proteins of interest, such as animal cells (e.g., CHO), insects (e.g., silk worm), insect cells, animals (e.g., chickens and cows), and microorganisms (e.g., E. coli and yeast), have been used in order to produce proteins via genetic recombination. In particular, yeasts can be cultured in large-scale, high-density culture systems in cost-effective media, and proteins can be produced at low cost. In addition, proteins can be secreted in a culture solution of yeast cells by using a signal peptide or the like, therefore, a process for purifying proteins is easy.
When a yeast host is used, however, heterologous protein production is not always satisfactory. Thus, improvement of protein productivity has been attempted through use of a potent promoter or improvement, such as reinforcement of chaperon functions via introduction of the chaperon gene, or disruption of a protease gene possessed by a yeast host.
Concerning heterologous protein secretion into a culture solution, an improvement in the productivity achieved via disruption of the vacuolar protein sorting (VPS) gene was reported in addition to the improvement described above.
While 61 types of VPS genes denoted as VPS1 to VSP75 are known to exist in the budding yeast Saccharomyces cerevisiae, all of such VPS genes are not effective. It is reported that the secretion productivity of a heterologous protein is improved via disruption of the particular VPS gene (Non-Patent Document 1; Patent Documents 1, 2, and 3).
In addition, genes that are effective to achieve the improved secretion productivity of a heterologous protein vary depending on yeast species. For example, disruption of the VPS10 gene is effective for the fission yeast Schizosaccharomyces pombe (Non-Patent Document 1), although such disruption is not effective for the budding yeast Saccharomyces cerevisiae (Patent Document 1).